I have a 23 y/o QH. He has the round and bulky QH build, but also has some dips behind his withers from age. I have had great luck with passier for his dressage saddle. I found a dominus CC (pre weatherbeeta days) that fits ‘ok’. I work with a fitter, and we’re still trying to adjust it properly for him. I’m not loving the dominus on me, so I’ve got my eyes out for a passier CC.
In my experience, saddles like the toulouse and the wintecs do not always fit the QH builds correctly as the gullet/panels tend to be too ‘A’ framed for their more rounded shoulders. However, If you have a QH that has strong thoroughbred lines, this type of fit may work. My guy is beefier, but another QH at my barn is thinner and might fit the more ‘A’ framed type panels. It really just depends on the horse.
How is his back, is it pretty straight or is he curvy? If he (or she ) has a curvier back, you may want to check out county, passier, and I believe stubben, as they have curvier trees.. If I remember right, thorowgood saddles also fall into this category (there’s a few others). You’ll want to stay away from saddles that tend to be flatter, such as toulouse, wintec, and pessoa. Although the wintec CC trees are curvier than their dressage trees, so you might be able to make it work if a wintec fits in the shoulders. Of course if your horse has a flatter back, then reverse the advice here!
Is the horse pretty symmetrical (not that any horse is EXACTLY symmetrical )? If they are, then foam panels may work for you. However, if the horse has some issues asymmetrically, I’d recommend wool flocked panels. The panels can be adjusted to fit your horse whereas foam panels cannot be adjusted. If you get a saddle with foam panels, you’ll have to correct for issues with pads. Of course you can use pads on wool panels too, but I personally like the saddle to fit without needing extra pads. Foam panels have really come into style, so newer brands/models, Pessoa for example, tend to focus more on foam than wool. Sometimes you can convert foam to wool, so keep that in mind as you search around.
Sorry for the small novel, but I hope this helps!